Mark Zuckerberg, Priscilla Chan expecting second baby girl

The Facebook CEO announced the news -- where else? -- in a Facebook post on Thursday. The couple welcomed their first daughter, Max, in 2015 after experiencing three miscarriages.

"After our difficult experience having Max, we weren't sure what to expect or whether we'd be able to have another child," Zuckerberg said in his post. "When Priscilla and I first found out she was pregnant again, our first hope was that the child would be healthy. My next hope was that it would be a girl."

That's in part because Zuckerberg has three sisters, while Chan has two.

"We are all better people because of the the strong women in our lives -- sisters, mothers and friends. We can't wait to welcome our new little one and do our best to raise another strong woman," Zuckerberg said.

When announcing Max's birth in 2015, Zuckerberg and Chan pledged to donate 99% of their Facebook stock to charitable causes.